undersize inverters?

[Ampster]

I'm not so sure about is how many panels are allowed on a single SE10000H to avoid clipping.

The SolarEdge designer "allows up to 1.55 to 1 DC to AC ratio. The algorithm is not designed to prevent clipping. I have a ration of 1.50 to one on my system. Yes I see some clipping but on overcast days I get good production and my system ramps faster.
Whether it is an undersized inverter or an over paneled system all depends on where you are standing. On an annual basis I have a good ratio between total kWhs output and system size based on panel capacity. It is interesting to note that a lot of commercial solar farms calculate their output ratios based on inverter size.

 

[zƬesla]

Wow, thread took off since I was last here

I have 17.5kW – 330W panels on 3 crankable poles (20, 15, 15) all facing south, two inverters (7.7, 7.0), and 2 PWs. The Tesla certified installer who designed the PW system (not the PV) indicated Tesla was ok with 7.6kW x # PWs, which is why we went with a 7.7 and 7.0 inverter instead of two 7.7s. When everything shutdown during a grid out test, they came back with it really being 7k x # PWs, then later said margin was really 5k X # PWs. Sadly, trusting the "certified" label is meaningless. I've been waiting on the installer to source another PW so we can increase it to 3 PWs total.

With the above system, 7.7 inverter has 3 strings of 10 panels each, and the 7.0 inverter has 2 strings of 10 panels each. Although I expected a little clipping, I ended up with what appears to be considerable clipping on the 7.7 and none on the 7.0, which now makes sense that I understand this better. Again, went with reputable PV installer and expected more knowledge on their part.

 

[Vines]

OP one more thing to understand is that STC is a flash of 1000 w/m^2, at 25 degrees C.

When comparing what modules actually do under the sun which also creates heat, use the PTC instead.

For instance the Q-cells 340 produces about 316 W at best in actual real world test conditions.

 

[Ampster]

Here are some other numbers
My panels 5.7 kW my inverter 3.8 kW DC to AC ration 1.5 to 1.
Annual production 8.84 kWhs
Annual panel capacity factor in kWhs - 1500 times panel capacity
Annual inverter capacity factor in kWhs - 2300 times inverter capacity
The other thing that was not discussed earlier is the busbar rating of the main service panel and whether that could handle a larger inverter(s).

 

[preilly44]

Thanks for the advice and info. I've asked Tesla how much more it would cost to upgrade to three 11.4kW inverters and for another PW. I'll decide once I get that info.

Side note, we don't have unlimited funds. We had a 19.25kw system on our last home (that was tore down and is being replaced by a larger home) and I still had a large electric bill every month. We have two electric cars, a pool, etc. that all use a lot of power. I want to over produce now to cover me in the future when we have a 3rd EV and the panels start to degrade. With that being said, I hate seeing clipping. I want to produce as much as possible.

Thanks again for your time and advice!

 

[CrazyRabbit]

Thanks for the quick responses. Just to give more information, there are several different roof directions (see layout below).

As far as the power walls go, it was my understanding that if I'm using enough power and the power walls are low enough, they will continue working and if I have one of my Tesla vehicles plugged in, any excess power would be used to charge the car. Should I be concerned? I'm trying to avoid adding more power walls because we probably won't be using them very often in the first place as we rarely lose power.View attachment 624951

with your amount of east west panels if properly wired you will NOT see any clipping.
34.2 kw may be harder for your utility to absorb, you might get rejected.

 

[jrweiss98020]

To put it in perspective from the view of a Seattle area user...

I have 27 x 335W panels for a total theoretical output of 9045W DC. I have Enphase IQ7+ microinverters, which total 7830VA AC continuous or 7965VA AC peak.

I have seen a peak output of 7940VA in April and June and 7900VA in August, which leads me to believe the microinverters rather than sun angle limit production for 2 months either side of Solstice. Looking at the peak production days, it appears there is about a 1:30 period around noon where the production is flat (i.e., clipped).

So, there is a total of about 180 hours/year where clipping COULD occur IF there were no cloud cover. That clipping seems to max out at less than 100VA (0.1 KW) judging by the shape of the curves, so that means a theoretical max production loss of 18 KWh/year due to clipping, which costs less than $2.00 total up here...

HOWEVER, in your case I would push for the 11.4 KW inverters, and also install a 4th Powerwall.

 

[TORQU3]

Thanks for the quick responses. Just to give more information, there are several different roof directions (see layout below).

As far as the power walls go, it was my understanding that if I'm using enough power and the power walls are low enough, they will continue working and if I have one of my Tesla vehicles plugged in, any excess power would be used to charge the car. Should I be concerned? I'm trying to avoid adding more power walls because we probably won't be using them very often in the first place as we rarely lose power.View attachment 624951

Why all the north facing panels (I count 24)? At $2/watt that’s about $16,000. I would think that would really kill your ROI time. It looks like you have two south facing open roof areas on your house and maybe some room south facing on your shed. Maybe try to move some there?

You may want to evaluate if it makes more sense removing north panels and maybe adding some power walls instead.

 

[h2ofun]

Why all the north facing panels (I count 24)? At $2/watt that’s about $16,000. I would think that would really kill your ROI time. It looks like you have two south facing open roof areas on your house and maybe some room south facing on your shed. Maybe try to move some there?

You may want to evaluate if it makes more sense removing north panels and maybe adding some power walls instead.

When I see homes that have put panels on the north facing roof, I just scratch my head. Same when I see panels on a east facing roof.
I have one north and I keep thinking if I were to ever put panels there, I would put them on tilts so they angled to the south. Am I missing something?

 

[nwdiver]

Am I missing something?

.... I thought you didn't care about ROI... are aesthetics also not a concern? Just kWh at any price? E/W only loses ~15% vs South facing. If you've used up all your South surfaces even N can be practical now that panels are ~$0.40/w.

 

[h2ofun]

.... I thought you didn't care about ROI... are aesthetics also not a concern? Just kWh at any price? E/W only loses ~15% vs South facing. If you've used up all your South surfaces even N can be practical now that panels are ~$0.40/w.

Depends on the time of day

What is your thoughts on aesthetics?

Luckily, I hope to not need anymore panels. Will see at end of July.

What is practical numbers with north? If I go down 75 to 80% in off season with south and west, what would north do?
What are north at best compared to south?

 

[nwdiver]

Depends on the time of day

What is your thoughts on aesthetics?

Luckily, I hope to not need anymore panels. Will see at end of July.

What is practical numbers with north? If I go down 75 to 80% in off season with south and west, what would north do?
What are north at best compared to south?

My two primary concerns are cost (ROI) and aesthetics. If solar isn't a good investment ~99% of people will not be interested. If solar makes their home look less appealing most people will not be interested. East and West panels may lose ~15% of annual production but they're a lot more attractive than panels that aren't flush to the roof.

You can play with PV Watts to determine the viability of North facing panels. The biggest benefit is that in the summer they can outperform other orientations in the late evening when production is more valuable since the sun actually sets to the North at some latitudes.

 

[h2ofun]

My two primary concerns are cost (ROI) and aesthetics. If solar isn't a good investment ~99% of people will not be interested. If solar makes their home look less appealing most people will not be interested. East and West panels may lose ~15% of annual production but they're a lot more attractive than panels that aren't flush to the roof.

You can play with PV Watts to determine the viability of North facing panels. The biggest benefit is that in the summer they can outperform other orientations in the late evening when production is more valuable since the sun actually sets to the North at some latitudes.

I agree, the tilt up panels look terrible, let alone issues with wind.

I just hope I do not need anymore

 

[preilly44]

Just to follow up about the north facing panels, I asked Tesla to max out the number of panels on both buildings. Unfortunately, the second building has a very steep roof on the west side, which why they didn't put any panels there. On the main house, they didn't put any panels on the southern most roof because they said the roof is to small to fit panels on (it broken up in to roof angles facing south, east and west). I'm still waiting to hear back from Tesla about the additional cost of going with the bigger inverter, just so I have all the info. I'll post it here when I hear from them.

I was just told by our builder that we are going to need to go with 800amp service. Does that change anything solar panel or power wall wise? I assume since I'll only be backing up 1 200amp panel it shouldn't change anything, right?

Thanks again for all your time and advice!

 

[jrweiss98020]

800 amps? Are you running an aluminum smelter in the house?!?

What are you backing up on 1/4 of the total service? Plan carefully, and consider whether you might want to back up 2 panels.

 

[Laketime]

I was just told by our builder that we are going to need to go with 800amp service. Does that change anything solar panel or power wall wise? I assume since I'll only be backing up 1 200amp panel it shouldn't change anything, right?

Thanks again for all your time and advice!

800amps? Thats enough to run 20-30 CAC units. Is this a home or a commercial building?

 

[Ampster]

I was just told by our builder that we are going to need to go with 800amp service.

Your builder must think you have unlimited funds. This sounds like a money grabbing change order request. Did he provide a rationale?

 

[h2ofun]

Your builder must think you have unlimited funds.

And I thought on my remodel I was doing some crazy stuff. 800 amps, in a house, never heard of that.

 

[preilly44]

Our builder said we are very close to maxing out 400amp service and there is no option for 600amp service so the next step up is 800amp service.

I've been debating backing up two 200amp panels but then I'd need at least 6 power walls because I don't think 2 power walls each would have enough output power (I think 5kw per pw). Thoughts?

 

[nwdiver]

Our builder said we are very close to maxing out 400amp service and there is no option for 600amp service so the next step up is 800amp service.

I've been debating backing up two 200amp panels but then I'd need at least 6 power walls because I don't think 2 power walls each would have enough output power (I think 5kw per pw). Thoughts?

What's using so much power? How many square feet is your house? Many builders I've encountered are..... how to put this delicately...... 'stuck in their ways...'. There may be obvious ways to reduce power use that your builder isn't considering....